Big Ben

CLEANED: Every five years or so Crew members scale the 316-foot-tall clock to scrub its four timepieces, each containing 312 pieces of opal glass. And time doesn’t stop: Workers dodge the moving minute and hour hands, which measure nearly 14 and nine feet long, respectively! The next scheduled cleaning is in 2016.

Acropolis Hill Sculptures

CLEANED: Daily In 2008, scientists set out to find the safest way to swab the 2,500- year-old marble statues. After testing 40 methods, they determined the winning technique was a combination of infrared lasers and ultraviolet rays. But the cleaning can be a dangerous job: Restorers wear goggles and operate the lasers for only two hours a day.

Statue of Liberty

CLEANED: Minimally Lady Liberty has dodged bath time for a while now—curators haven’t cleaned her exterior in years because infrequent cleaning aids in her preservation. The inside gets scrubbed frequently, however, which is how the statue developed “birthmarks”—an acidic solution leaked through the inside wall and stained her cheek in 1986.